Method of forming particulate material



Se t. 1, 1959 I A. T. DEUTSCH 2,902,364

METHOD OF FORMING PARTICULATE MATERIAL Filed Sept. 19, 1957 2Sheets-Sheet 1 & {NW

% r 5 T i 8 F? M w I V 11 I I Q A/exanaer raw/$6 l1 7 INVENTOR ATTORNEYjSept. 1, 1959 A. 'r. DEUTSCH 2,902,364

METHOD OF FORMING PARTICULATE MATERIAL Filed Sept. 19, 1957 2Sheets-Sheet 2 INVENTOR ATTORNEY5 United States atet 2,902,364 METHOD.OFFORMING PARTICULATE MATERIAL terials' which are in a powdered,particulate or generally subdivided state.

' During the past twenty years'the technology of powder metallurgy hasundergone a rapid and increasingly accelerated growth until, at thepresent date, a large volume of metal parts is manufactured by powdermetallurgy techniques. Sintering is undoubtedly the most widely used ofthese techniques and is based upon two basic phenomena. The first isthat finely divided metal powders willbond together weakly whencompounded at high pressure; and the second is that such compactedpowders will bond together strongly when heated to relatively hightemperatures under controlled conditions. '=-In a conventional sinteringprocess of this type, the metal powders are blended ormixed in atumbling barrel and then transferred to either a briquetting or acontinuous extrusion press. ess; the powder is introduced into a die andis compacted therein at a pressure on the order of 30 tons *per squareinch. The formed object is then removed -firom the press'more or less ina fragile state and is introduced into a'sintering furnace which mayoperate at t a temperature of around 2000 F. under a reducing atmosphereto reduce theoxides present in the compact as-well as preventtheirformation. In addition to being applicable to-metals, such. sinteringprocesses are also useful with the so-calledcermets which are aggregate"structures of hard and refractory substances bonded with "metal.

In a typical impact press proc- A sinteringprocessofthe foregoing typeis disclosed in United States Patent No. 2,289,787 which utilizes acombined compacting and extruding ram for forming a r solid,self-sustaining rod which is thence fed to some suitable-heating devicefor producing the desired sinter- 1 ing temperature.

shows :aprocess of asimilar typewherein the compacting and extrudingpressures are separately applied.

United States Patent No. 2,447,129

T he density of the articles which can be produced by the foregoingsintering process is limited and any improvement in this densitynecessitates additional method --steps such as re-pressing or coining.Some metals, however, such as uranium, are not improved by these addi---.-tional*steps and thus cannot be conveniently handled bysintering'processes of the foregoing general type.

I have now found that it is possible to produce improve'dmetal andceramic objects from powders, pellets, chips or other particles withoutthe aforementioned additio'nal steps in a basically different manner.According to my invention, the material particles are compacted orcompressed in the same general manner as is customary P in-theconventional powdered metal forming and sintering processes, except thatthe extremely high pressures used in thoseprocesses are not necessary.That is to 1 say, my process does not depend upon the initial weak bondproduced by the high pressures of previous processes, and I only desireto secure a reduction in volume of about /6 at this stage of my process.Instead of then extruding and/ or sintering, I subject the compactedparticles in an unheated state to a forging or pounding action to causea reduction or refinement of particle size.

Subsequent to the start of this particle reduction step, I

\ direct radiant energy, such as heat or high frequency radiation, intothe mass of particles which causes diffusion to occur at the individualparticle interfaces.

The

2 material then assumes an extremely dense, condition and may beextruded or molded to form metaland ceramic objects having qualities ofa vastly improved nature. By diffusion I refer to the diffusion of atomsfrom one particle into its adjacent particle as that term is understoodby those skilled in the art and as is explained, for example, inScientific American,'May 1957, pages, l03110.

It is accordingly a primary object of the present invention to providean improved process for producing metal or ceramic parts from subdividedor particulate materials.

It is another object of the invention to, provideqan improved processfor producing metal or ,CQramicparts from subdivided or particulatematerialsrwhich includes the steps of compacting the subdividedmaterial, reducing the size of the particles of such material, andcausing diffusion at the contacting interfaces of adjacent, particles ofthe material.

These and further objects and advantages of the invention will becomemore apparent upon referenceto the following specification and claimsand appended drawings wherein:

Figure 1 is a vertical cross section showing one. embodiment of a devicefor performingthe process of the invention;

Figure 2 is a vertical section of another, embodiment of an apparatusfor performing the process of the. invention;

Figure 3 is a vertical elevation of still another embodiment of anapparatus for performing the process of the invention;

Figure 4 is a photomicrograph of a compacted metal; and

Figure 5 is a photomicrograph of a metaLcompacted, forged and diffusedaccording to the invention.

' The particles used in the. process of the invention may be particlesof metals, mixtures of metals, ceramics, mixtures of ceramics orcermets, and may be in the form of fine powders, chips or pellets. Theparticles are cleaned in any suitable manner to remove oxidation orother impurities upon their surfaces and this may conveniently beaccomplished with hydrogen at a temperature of about 1000 F. in a knownmanner. The particles are thereafter preferably maintained in acontrolled atmosphere such as inert gases or a vacuum to prevent furtheroxidation as is understood by those skilled in the art. This controlledatmosphere may be advantageously maintained throughout the process. Thecompacting step is then carried out by a light hammering to produce areduction in volume of about /6. The precise manner of pressureapplication and the specific pressures used are not critical so long asthe initial reduction in volume of about /6 is obtained. This compactioncauses the finely divided metal powders to bond together weakly in thesame general manner as does the compaction step in conventionalsintering processes and produces a structure illustrated in thephotomicrograph shown in Figure 4. This photomicrograph is alsoillustrative of the type structure obtained in the compacting step ofconventional sintering processes. It is to be noted that this. structureis relatively porous and, generally speaking, it is impossible tocompletely eliminate this porosity through the application of practicalamounts of increased pressure.

According to the next step of the process of my invention, the crystalsor particles are refined or subdivided along their glide lines and Ihave found that this may be efiectively accomplished by hammering. Thedesired refining or subdivision of the particles may be obtained byhammering the compacted material with a 250 lb. hammer with a face ofabout 1 square inch which achieves a maximum velocity of 30 ft. persecond and is reciprocated at about 5-30 hammer strokes per minute. Eachstroke produces a maximum energy of approximately 3460 ft.-lbs. andproduces a new structure which is illustrated in the photomicrograph ofFigure 5. It is to be noted that the particle size has been greatlyreduced from that which existed in the compacted structure of Figure 4and that the individual particles are in much more intimate and closecontact with one another.

The temperature of the mass undergoing the hammering is now raised to avalue several hundred degrees below the melting point of the powderhaving the lowest melting point in the material and the hammeringcontinued. The heat causes an accelerated diflusion at the interfaces ofthe particles and the volume of the mass is reduced to about of itsoriginal volume. The heat may be applied through combustion, heatedfluids, induction heating, or other radiated types of energy such asinfra-red or ultrasonic sound. In its broadest aspect my inventioncomprehends the introduction of energy into the material to cause thisaccelerated diffusion regardless of the manner in which such energy isintroduced or its precise nature. When the material reaches a volumeabout of its original volume, it is cooled to form a high quality denseproduct with excellent physical characteristics. The initial compactionand at least the beginning of the forging step are carried out with thematerial unheated. In order to prevent the material from welding to thedie, the internal surface of the die may be coated with resin asshellac.

As one example of a metal extrusion produced according to the process ofthe invention, high quality steel parts have been formed having a yieldstrength of 200,000 p.s.i. These parts were formed using 37.5% HoeganesW/428 sponge iron powder, Tyler mesh plus 62 to plus 200, density 2.8gms. per cc.; 3% fine mesh copper; 1.5% oxygen absorbing aluminum, 20%nickel, 20% chromium, 18% cobalt. This material was compacted in a dieunder relatively light hammer blows until the volume of the material wasreduced by /6. Hammering then was commenced at a rate of strokes perminute at approximately 3,000 ft. lbs. of energy per stroke. Thetemperature of the mass in the die was raised to 1100" F. throughinduction heating and the volume of the mass finally reduced to about ofits original volume in between two and three minutes. The material wasthen air-cooled and removed from the die and exhibited a yield strengthof 200,000 p.s.i.

According to another example of the process of the invention, a powderconsisting of 35% electrolytic iron, aluminum, 30% nickel, 10%manganese, 5% copper and 5% zinc was subjected to the same process andalso produced excellent specimens.

According to still another example, small chips produced in the millingof structural steel and aluminum were shaped into high density parts,having strengths equal to the original strengths of the material, attemperatures of 1100 F. and 800 F. respectively, the other steps in theprocess being the same as set out hereinbefore.

Referring to Figure 1 of the drawing, there is shown a vertical sectionof an extrusion press which may be used in carrying out the process ofthe invention. An extrusion press chamber 10 having a nozzle 12 at oneend thereof is abutted by a movable stop plate or gate 14 having asuitable actuating rod 16. The stop plate or gate 14 is backed up by anaperture plate 18 which is stationarily mounted to hold the stop plateor gate against pressure created within the extrusion chamber. An inlethopper 20 is provided at the top of the extrusion chamber and suitableheating passages 22 are provided within the chamber and nozzle walls.The extrusion chamber is mounted on a suitable standard 24 on a base 26.

The other end of the base 26 carries an extrusion cylinder 28 in whichan extrusion piston 30 is received. The extrusion piston 30 isreciprocable in cylinder 28 and may be moved leftward by means of asuitable fluid introduced in the cylinder through an inlet aperture 32at the right end of the cylinder. The left end of the extrusion pistonis bored at 34 and receives a forging piston 36 which is mounted forreciprocation. Fluid passages 38 and 40 provide communication betweenthe bore and a three-way valve 42 which connects these passages to afluid supply 44. By suitable actuation of the valve 42 the piston 36 maybe made to oscillate in a known manner. The outward end of the piston 34carries a piston head 46 which may be made heavy enough to provide thehammering energy desired.

Mounted parallel to the extrusion piston 30 are a pair of returncylinders 48 and 50 which carry pistons'52 and 54 and which areconnected to the extrusion piston 30 by means of piston rods 56 and 58and cars 60 and 62. Suitable fluid connections for the return cylindersare provided at 64 and 66, 68 and 70.

The operation of this embodiment of the invention is as follows: Thestop plate or gate 14 is closed and a clean powdered material such aspowdered metal is introduced into the extrusion chamber 12 through thehopper 20. Fluid passage 40 leading to bore 34 in extrusion piston 30 isopened and fluid introduced into the extrusion cylinder 28 through theinlet 32. This causes the extrusion piston 30 to move to the leftthereby compressing the powdered metal introduced through the hopper 20.The piston head 46 moves to the right until the rear end of the forgingpiston 36 strikes the end of the bore 34. Since the stop plate or gate14 is closed it is possible to compact the powdered metal under thedesired high pressure. After this has been accomplished, the extrusionpiston 30 may be withdrawn to the right for a slight distance throughactuation of cylinders 48 and 50 and fluid pressure applied to the backof forging piston 36. By repetitive actuation of the forging pistoncontrol valve 42, the piston head 46 is caused to strike repeated blowsagainst the compacted powder. By controlling the weight of the pistonhead 46 and its piston 36 and the pressure of the fluid introduced intothe forging piston bore 34, it is possible to obtain the desired energyin the impact of the hammer in order to reduce and refine the size ofthe particles of material.

After forging has been commenced heat is introduced into the extrusionchamber through the heating conduits 22 and the temperature of the massraised until the diffusion occurs at the particle interfaces. After thisstate of the material has been reached, the stop plate or gate 14 may beraised and the material extruded through the nozzle 12 by introducingfurther fluid behind the extrusion piston 30. It will be understood thatonce the process has been performed the nozzle 12 will contain cold hardmetal which will seal the press for the next compaction so that the gate14 is thereafter unnecessary.

Referring to Figure 2, there is shown another embodiment of theinvention in which the compacting and hammering or forging may beeffected by means of the same piston. In this embodiment of theinvention the extrusion chamber, nozzle, stop plate and hopper are thesame as in the preceding embodiment of the invention and thus bear thesame reference numerals. Induction heating may be used with thisembodiment of the invention and thus the heating channel 22 of Figure 1has been eliminated. According to this embodiment an extrusion pistoncylinder 72 is connected to the extrusion chamber 10 by means ofsuitable flanges and bolts, indicated at 74, and carries a piston 76.The piston 76 is milled away at 78 to form a reduced diameter sectionand this communicates with a fluid supply conduit 80 through an aperture81 in the piston cylinder wall. A second conduit 82 is connected to theback of the cylinder 72 through an aperture 84, and conduits 80 and 82are connected to a suit- ;able control valve 86.

A further inlet 88 is provided at the rear of the cylinder 72 forsupplying the fluid which applies the high compacting and extrusionpressure. A suitable guide rod 90 extends through the rear of thecylinder 72 through suitable packing means. It will be apparent to thoseskilled in the art that hydraulic fluid can enter the cylinder 72through conduit 88 to force the piston 76 to the left to compact thepowdered material; that this hydraulic fluid can then be exhausted fromthe cylinder by moving the piston to the right under control of fluidfrom conduit 80; and that the piston 76 can be oscillated orreciprocated through suitable actuation of the valve 86 to cause ahammering of the compacted material. Hydraulic fluid can then bereintroduced through conduit 88 to extrude the material from theextrusion compartment 10.

Referring to Figure 3, there is shown a further embodiment of theinvention comprising a vertical press suitable for carrying out theprocess. According to this embodiment of the invention, the lowercylinder 96 is mounted in a stand 98 having an upper flange 100. Thecylinder 96 carries a back-up piston 102 which extends through (theflange 100 into an extrusion die 104 and which is supported by fluidwhich enters through a port 105. The extrusion die 104 is secured to theflange 100 by means of a [flange 106 and contains an extrusion chamber108 which receives the upper end of the piston 102. The die may be ofthe split type which is openable to permit removal of the piece formedtherein. A suitable induction heating coil 110 is mounted about theextrusion die cavity and is connected to a suitable source of highfrequency induction heating power. A smaller bore 112 extends out of thetop of the extrusion die and receives the end of an upper piston 114.Suitable packing 116 and 118 is provided in the die in a conventionalmanner.

The upper piston 114 is carried by the upper piston assembly 120 whichrests upon standards 118 on flange 100. Assembly 120 is mounted onstandards 118 by means of a lower flange 122 through which a hollow ram124 extends. The ram 124 passes through packing 126 in the flange 122and through packing 128 at the upper end of a cylinder 130 which ismounted on the flange 122. A piston head 132 is provided about the ram124 in the cylinder 130 for movement of the ram under the influence offluids introduced into the cylinder 130 through apertures 134 and 135. Apair of return cylinders 136 and 138 are mounted at either side of thecylinder 130 and have pistons 130 and 132 mounted therein and connectedto the ram by brackets 144. Apertures 145 in cylinders 136 and 138provide hydraulic connections for raising the cam 124.

The upper piston 114 extends into the ram 124 and carries a stop flange146 which abuts the lower end of the ram 124. The upper end of thepiston 114 is connected to a piston head 148 which is received within acylinder 150 mounted atop the upper piston assembly 120. Conduits 152and 154 connect this piston to a valve 156 and fluid supply 158 forreciprocating the piston head 148 and piston 114.

The operation of this embodiment of the invention is as follows: Asuitable powdered material is introduced into the split die 104 on topof the lower piston 102. The upper ram 124 is then moved downwardly byfluid pressure introduced in back of piston head 132 and this carriesthe piston 114 downwardly by reason of the abutment of flange 146against the lower end of the ram 124. Compaction of the powderedmaterial is carried out in this manner to the desired degree. The upperram may then be maintained in this position by means of fluid pressurein cylinder 130, or other positive locking means, and the piston 114caused to reciprocate by means of actuation of the valve 156. Thiscreates the desired hammering or forging and heat may be introduced bythe induction heating coil 110. When the forging step 1s completed, thepiston 114 may be withdrawn from the die by appropriate actuation ofvalve 156, and the piece removed from the die.

While specific presses have been described herein, rt

be understood that this has been by way of illustration only and is notmeant to be limiting in any respect. That is to say, the process of myinvention may be carried out in conventional presses or may be carriedout with the newer presses designed to handle the newer high temperaturealloys. Since my process involves heating the material to within a fewhundred degrees of its melting temperature, it is obvious that thepresses utilized must be capable of withstanding such temperatures.Similarly while the process of the invention has been described in termsof forming specific articles, it is not limited to this but may be usedfor other purposes, such as forming a layer of one type of metal uponanother, or similar uses. Again, while the injection of energy into thematerial in order to cause accelerated diflusion has been primarilydiscussed in terms of heat, it is to be understood that the inventionalso encompasses and includes the addition or injection of atomic ornuclear energy derived from radiative isotopes or other sources in orderto accelerate difiusion. The acceleration of diflusion is one of thebasic steps of my process and the invention comprehends all methods ofenergy addition or injection which have this effect.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

This application is a continuation in part of my copending applicationSer. No. 603,421, filed August 10, 1956, now abandoned.

What is claimed and desired to be secured by United States LettersPatent is:

1. The method of forming particulate metallic material comprisingcompacting said material and performing on said compacted material thecontinuous sequential steps of impacting said material in asubstantially cold state to cause a refining of the particle size,introducing into said material as said impacting continues controlledheat energy other than friction heat, and continuing said impacting andthe introduction of said heat energy to cause accelerated soliddiflusion at the interfaces of the refined particles and a reduction ofthe volume of the material, the introduction of said heat beingcontrolled to maintain the temperature of the mass below the meltingtemperature.

2. The method of forming particulate material according to claim 1including the additional continuous sequential steps of extruding saidmaterial.

3. The method of forming particulate material according to claim 1wherein said impacting is carried out while said material is maintainedin a confined space.

4. The method of forming particulate metallic material according toclaim 3 including the additional continuous sequential step of extrudingsaid material from said confined space.

5. The method of forming particulate metallic material according toclaim 4 wherein said material is extruded through a die.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Goetzel: Treatise on Powder Metallurgy, vol. 1,

PP- 306-312, 459, 460. t

STATES PATENT OFFICE UNITED CERTIFICATE OF CORRECTION September 1, 1959or appears in the prints d Letters certified that err ered patentrequiring correction a d that the sai s corrected below.

It is hereby of the above numb Patent should read a line 72, for

Golinnn 1, line 25, for "impact" read compacting "particle readparticles Signed and sealed this 19th day of Januaryil960,

\ (SEAL) Attest'.

) ROBERT c. WATSON 1 KARL H. .AXLINE Attesting Ofiicer Commissioner ofPatents Patent No. 2,902,364

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION September 1, 1959Alexander T, Deutsch It is herebfi certified that error appears in theprinted specification of the above numbered patent requiring correctionand that the said Letters Patent should read as corrected below.

Colinnn 1, line 25, for "impact" read compacting line '72, for"particle" read particles Signed and sealed this 19th day ofJanuaryll960.

(SEAL) Attest:

KARL Hm AXLINE Attesting Officer ROBERT C. WATSON Commissioner ofPatents

1. THE METHOD OF FORMING PARTICULATE METALLIC MATERIAL COMPRISINGCONPACTING SAID MATERIAL AND PERFORMING ON SAID COMPACTED MATERIAL THECONTINUOUS SEQUENTIAL STEPS OF IMPACTING SAID MATERIAL IN ASUBSTANTIALLY COLD STATE TO CAUSE A REFINING OF THE PARTICLE SIZE,INTRODICING INTO SAID MATERIAL AS SAID IMPACTING CONTINUES CONTROLLEDHEAT ENERGY OTHER THAN FRICTION HEAT, AND CONTINUING SAID IMPACTING ANDTHE INTRODUCTION OF SAID HEAT ENERGY TO CAUSE ACCELERAND A REDUCTION OFTHE VOLUME OF THE MATERIAL, THE INTRODUCTION OF SAID HEAT BEINGCONTROLLED TO MAINTAIN THE TEMPERATURE OF THE MASS BELOW THE MELTINGTEMPERATURE.